(i) Field of the Invention
The present invention relates to a scroll type fluid machine which can be employed as a compressor, an expanding machine, an electric motor or the like, and to a method for molding scroll members used in the fluid machine.
(ii) Description of the Prior Art
FIGS. 19 and 20 (which is a sectional view taken along the line XX--XX in FIG. 19) of accompanying drawings show one embodiment of a scroll body in a conventional scroll type compressor. A pair of scroll bodies 01, 02 are engaged with each other, with their laps 01a, 02a deviating from each other in phase as much as an angle of 180.degree., and with tip ends 01c, 02c of the laps 01a, 02a closely contacting with inside surfaces 01d, 02d of side plates 01b, 02b. In consequence, when both the scroll bodies are revolved relatively, fluid volumes in sealed chambers 03, 04 defined by the pair of engaged scroll bodies 01, 02 will be reduced gradually while they are moved toward their center, in order to compress a gas in the chambers 03, 04 and to then discharge it through a discharge opening 05 at the central position of the machine.
Techniques for manufacturing this type of scroll members 01, 02 can be classified into two methods. One of them comprises separately preparing the side plates and the laps, and then combining both to each other. Another method comprises simultaneously and integrally preparing the side plates and the laps. In the case of the former method, the technique of fixing the laps to the side plates is less reliable and a working accuracy is also insufficient, and thus the side plates and the laps, after their fixation, must be finally finished on all of their surfaces which will be in contact with the partner scroll. For this reason, the method in which the scroll members 01, 02 are integrally and simultagenously formed has heretofore been employed.
However, the conventional integral type of fluid machine takes the system that the gas in the sealed chambers 03, 04 is airtightly retained, therefore as shown enlargedly in FIG. 21, angular portions at the corner of base portions of the laps 01a, 02a and inside surfaces 01d, 02d of the side plates 01b, 02b cannot be rounded and have right angles. As a result, stress will concentrate at these angular corner portions, and the base portions of the laps 01a, 02a will be poor in strength, depending upon a height of the laps 01a, 02a and compressive conditions. Further, a repeated application of an engaging force between the laps 01a, 02a and/or a pressure of the gas in the sealed chambers 03, 04 will lead to the occurrence of cracks and breakage troubles. It can thus be appreciated that the conventional integral method possesses no satisfactory reliability.
The pressure of the gas in the sealed chambers 03, 04 becomes higher as the sealed chambers 03, 04 approach the center of the spiral laps, and it is to be noted that the siffness of the spiral laps 01a, 02a is smaller at their inner end portions, i.e., at their central portions than at other portions thereof. In most cases, accordingly, cracks and breakage troubles have appeared at a base of an inner end portion (at an end in the center of a spiral eddy) of each lap 01a or 02a, as shown by an arrow in FIG. 23.
If an attempt is made to round the angular portions A.sub.2 at the corners of the bases of the laps 01a, 02a and the inside surfaces 01d, 02d of the side plates 01b, 02b on condition that the gas in the sealed chambers 03, 04 is airtightly retained, a constitution in FIG. 22 can be conceived.
Moreover, as in FIG. 22, if it is contemplated to round the angular portion at the base corner A.sub.2 of the lap 01a of the scroll members 01 and the inside surface 01b of the side plate 01b, the respective laps 01a, 02a of the pair of scroll members 01, 02 must also be rounded on their tip portions B.sub.2 in order to prevent the angular portion A.sub.2 from contacting with the tip portion of the lap 02a of the partner scroll member 02.
In short, it is necessary to round off, in the same shape, the angular portions A.sub.2 at the corners of the laps 01a, 02a and the side plates 01b, 02b of both the scroll members 01, 02 as well as the tip portions B.sub.2 of the corresponding laps 01a, 02a.
In order to obtain such a structure, an extremely intricate working will be required and costs of the mechanical working will increase noticeably. For this reason, such a constitution can be designed only on a desk, but has not been put into practice.